The invention relates to the alkylation of aromatic compounds with olefins using solid catalyst
About thirty years ago it became apparent that household laundry detergents made of heavily branched alkylbenzene sulfonates were gradually polluting rivers and lakes. Solution of the problem led to the manufacture of detergents made of linear alkylbenzene sulfonates (LABS) and later modified linear alkylbenzene sulfonates (MLABS), both of which were found to biodegrade more rapidly than the heavily branched variety. Today, detergents made using LABS and MLABS are known.
LABS are manufactured from linear alkylbenzenes (LAB), and MLABS can be made from modified linear alkylbenzenes (MLAB). The petrochemical industry produces LAB by dehydrogenating linear paraffins to linear olefins and then alkylating benzene with the linear olefins in the presence of HF. This is the industry""s standard process.
Over the last decade, environmental concerns over HF have increased, leading to a search for substitute processes employing catalysts other than HF that are equivalent or superior to the standard process. Solid alkylation catalysis to produce LAB, for example, is the subject of vigorous, ongoing research. Solid alkylation catalysts can also be used to produce MLAB and are also being researched vigorously. It is known that MLAB may be made by dehydrogenating slightly branched paraffins to slightly branched olefins and then alkylating benzene with the slightly branched olefins in the presence of a solid catalyst. See, for example, U.S. Pat. Nos. 6,111,158 B1 and 6,187,981 B1, which are incorporated herein by reference.
As desirable as solid catalyst may be as an alternative to liquid HF, it is commonly the case that these catalysts deactivate with use. All alkylation catalysts, including HF and substitute catalysts for HF, lose some portion of their activity with continued use. However, the solid catalysts used to date in aromatic alkylation tend to deactivate rather quickly. Solid catalysts used for alkylation of -aromatic compounds by olefins, especially those in the 6 to 22 carbon atom range, usually are deactivated by gum-type materials that accumulate on the surface of the catalyst and block reaction sites. These materials include byproducts, such as aromatic (including polynuclear) hydrocarbons in the 10 to 22 carbon atom range, that are formed in the dehydrogenation of C6 to C22 paraffins. These materials also include undesired alkylation byproducts of higher molecular weight than the desired monoalkyl benzenes, e.g., di- and tri-alkyl benzenes, as well as olefin holigomers and other olefinic compounds.
An alkylation process using a solid alkylation catalyst typically includes means for periodically taking the catalyst out of service and regenerating it by removing these deactivating materials from the catalyst. For a solid alkylation catalyst, the catalyst life is measured in terms of time in service at constant conversion between regenerations. The longer the time between regenerations, the more desirable the catalyst and the process. Thus, it is clear that solid catalyst can be best used in the continuous alkylation of aromatics only where effective and inexpensive means of catalyst regeneration are available. Fortunately it has been observed that the deactivating materials can be readily desorbed from the catalyst by washing the catalyst with the aromatic reactant (e.g., benzene). Thus, catalyst reactivation, or catalyst regeneration as the term is more commonly employed, is conveniently effected by flushing the catalyst with an aromatic such as benzene to remove the accumulated deactivating materials from the catalyst surface, generally with restoration of 100% of catalyst activity.
A typical prior art means for regenerating the solid catalyst in an aromatic alkylation process is described in U.S. Pat. No. 6,069,285. The effluent of an alkylation reactor undergoing regeneration combines with the effluent of an on-stream alkylation reactor, and the combined effluent passes to a section of the process for recovering benzene, the alkylated benzene product, and other streams. In U.S. Pat. No. 6,069,285, this section comprises a benzene rectifier, a benzene fractionation column, and other product recovery facilities. Part of the benzene recovered from this section is recycled to the off-stream alkylation reactor to regenerate the deactivated catalyst. Another prior art process passes the effluent of the reactor undergoing regeneration to a separation zone to reject color bodies and to recover benzene that passes to the benzene fractionation column of this section.
Besides regeneration, another means for maintaining high catalyst activity is to prevent the previously mentioned aromatic byproducts formed in the dehydrogenation of paraffins from ever entering the alkylation reactors. These aromatic byproducts are believed to include, for example, alkylated benzenes, naphthalenes, other polynuclear aromatics, alkylated polynuclear hydrocarbons in the C10-C15 range, indanes, and tetralins, that is, they are aromatics of the same carbon number as the paraffin being dehydrogenated and may be, viewed as aromatized normal paraffins. They are typically removed using an aromatics removal zone, such as those described in U.S. Pat. Nos. 5,276,231; 5,334,793; and 6,069,285, the contents of which are incorporated herein by reference. Fixed bed sorptive separation zones that use a particulate sorbent, such as a molecular sieve (e.g., 13 X zeolite (sodium zeolite X)), are the most common aromatics removal zones.
In a typical fixed bed system, the sorbent is installed in two or more vessels in a parallel flow arrangement, so that when the sorbent bed in one vessel is spent by the accumulation of the aromatic byproducts thereon, the spent vessel is bypassed while continuing uninterrupted operation through another vessel. A purge stream comprising a purge component, such as C5 or C6 paraffin (e.g., normal pentane), is passed through the spent sorbent bed in the bypassed vessel in order to purge or displace unsorbed components of the stream containing the aromatic byproducts from the void volume between particles of sorbent. After purging, a regenerant or desorbent stream comprising a desorbent component such as C6 or C7 aromatic (e.g., benzene), is passed through the sorbent bed in the bypassed vessel in order to desorb aromatic byproducts from the sorbent. Following regeneration, the sorbent bed in the bypassed vessel is again available for use in sorbing aromatic byproducts.
Thus, a sorptive separation zone for removing the aromatic, byproducts typically produces three effluents, which approximately correspond to each of the three steps in the cycle of sorption, purge, and desorption. The composition of each of the three effluents can change during the course of each step. The first effluent, the sorption effluent, contains unsorbed components (i.e., paraffins and olefins) of the stream from which the aromatic byproducts are removed, and also typically contains the desorbent component With its decreased amount of aromatic byproducts relative to the stream that is passed to the sorptive separation zone, this effluent is used farther along in the process to produce alkylaromatics. For example, if the stream that passes to the sorptive separation zone is the dehydrogenation zone effluent, the sorption effluent contains monoolefins and paraffins and thus passes directly to the alkylation zone.
The second effluent, the purging effluent, contains the purge component, unsorbed components of the stream from which the aromatic byproducts were sorbed, and often the desorbent component. The third effluent is the desorption effluent, which contains the desorbent component, the aromatic byproducts, and the purge component The purging and desorption effluents typically are separated in two distillation columns. The desorption effluent passes to one column, which produces an overhead stream containing the desorbent and purge components and a bottom stream containing the aromatic byproducts which is rejected from the process. The overhead stream of the first column and the purging effluent pass to a second column, which separates the entering hydrocarbons into an overhead stream containing the purge component and a bottom stream containing the desorbent component and unsorbed components of the stream from which the aromatic byproducts are removed. The overhead stream of the second column is used as the purge stream. The bottom stream of the second column is used in the process to produce alkylaromatics. In the example described above where the stream that passes to the sorptive separation zone is the dehydrogenation zone effluent, the bottom stream of the second column contains benzene, monoolefins, and paraffins and flows directly to the alkylation zone. Some of the benzene in this bottom stream passes through the alkylation reactor unreacted, and is recovered in the previously mentioned section for separating the alkylation reactor effluent.
Unfortunately, the prior art uses benzene inefficiently. Separating, recovering, and recycling benzene for the on-stream alkylation reactor is a huge cost by itself. But the prior art requires much more than just that amount of benzene, because of the benzene for catalyst regeneration and/or sorbent desorption. The rewards of large reductions in capital investment and operating expenses are the incentive to developing new ways to use benzene more efficiently in, aromatic alkylation processes.
This invention is a solid catalyst alkylation process that makes multiple uses of feed aromatic that is used to regenerate the catalyst. In one embodiment of this invention, feed aromatic in the effluent of an off-stream reactor that is undergoing regeneration passes without a separation step to an on-stream alkylation reactor. Thus, feed aromatic from regeneration is re-used for alkylation. In a second embodiment, feed aromatic in the effluent of an off-stream reactor passes without an intermediate separation to a sorbent bed that is undergoing desorption. In this way, feed aromatic from regeneration is re-used for desorption. In a variation of this second embodiment, some of the feed aromatic in the effluent of the sorbent bed that is undergoing desorption passes to an, on-stream reactor, so that feed aromatic in the sorbent bed effluent is used for a total of three times before passing to the product recovery section. In this variation of the second embodiment, preferably the effluent of the sorbent bed undergoing regeneration passes to a separation section associated with the sorbent bed, and a stream comprising the feed aromatic is recovered from the separation section and passes to the on-stream reactor. All of these embodiments save capital investment and operating expenses compared to the prior art processes, since unnecessary separation, recovery, and recycling of benzene are eliminated.
A broad objective of this invention is to produce alkylated aromatics. Another objective is to make alkylated aromatics using a solid alkylation catalyst. A Third objective is to produce alkylated benzenes in a process that uses benzene more efficiently or for more uses than the prior art processes. A fourth objective is to reduce contamination by color bodies or olefinic compounds of the on-stream alkylation reactor effluent and/or the product alkylated benzenes.
Accordingly, in one embodiment this invention is a process for producing a product aromatic compound. An aromatic feed stream comprising a feed aromatic compound and an olefinic feed stream comprising the monoolefin pass to an on-stream selective alkylation reactor. In the on-stream selective alkylation reactor, the feed aromatic compound is selectively alkylated by reacting the feed aromatic compound and the monoolefin in the presence of a solid alkylation catalyst at alkylation conditions to form a product aromatic compound. The alkylation conditions are sufficient to at least partially deactivate the solid alkylation catalyst An on-stream reactor effluent stream comprising the product aromatic compound is recovered from the on-stream selective alkylation reactor. At least a portion of the on-stream reactor effluent stream passes to a product recovery section. An alkylated product stream comprising the product aromatic compound is recovered from the product recovery section. A regenerant stream comprising the feed aromatic compound passes to an off-stream selective alkylation reactor containing the solid alkylation catalyst, which is at least partially deactivated. The off-stream selective alkylation reactor operates at regeneration conditions sufficient to at least partially reactivate the solid alkylation catalyst. An off-stream reactor effluent stream comprising the feed aromatic compound is recovered from the off-stream selective alkylation reactor. At least some of the feed, aromatic compound in the off-stream reactor effluent stream passes to the on-stream selective alkylation reactor before passing to the product recovery section. The functions of the on-stream selective alkylation reactor and the off-stream selective alkylation reactor are at east intermittently shifted by operating the on-stream selective alkylation reactor to function as the off-stream selective alkylation reactor and operating the off-stream selective alkylation reactor to function as the on-stream selective alkylation reactor.
In another embodiment, this invention is a process for producing a product aromatic compound, A C6-C22 paraffinic compound is dehydrogenated in a dehydrogenation zone and a monoolefin is recovered from the dehydrogenation zone. Aromatic byproducts are formed during the dehydrogenation of the C6-C22 paraffinic compound. A dehydrogenation effluent stream comprising the paraffinic compound,, the monoolefin, and the aromatic byproducts is recovered from the dehydrogenation zone. The dehydrogenation effluent stream has a first concentration of the aromatic byproducts. Some of the aromatic byproducts are selectively removed from at least a portion of the dehydrogenation effluent stream in an on-stream aromatic byproducts removal bed. The on-stream aromatic byproducts removal bed contains a sorbent operating at sorption conditions effective to selectively sorb the aromatic byproducts. An on-stream bed effluent stream comprising the monoolefin is recovered from the on-stream aromatic byproducts removal bed. The on-stream bed effluent stream has a second concentration of the aromatic byproducts that is less than the first concentration. An olefinic feed stream comprising the monoolefin is formed from at least some of the on-stream bed effluent stream. The olefinic feed stream and an aromatic feed stream comprising a feed aromatic compound pass to an on-stream selective alkylation reactor. In the on-stream selective alkylation reactor, the feed aromatic compound is selectively alkylated by reacting the feed aromatic compound and the monoolefin in the presence of a solid alkylation catalyst at alkylation conditions to form a product aromatic compound. The alkylation conditions are sufficient to at least partially deactivate the solid alkylation: catalyst. An on-stream reactor effluent stream comprising the product aromatic compound is recovered from the on-stream selective alkylation reactor. At least a portion of the on-stream reactor effluent stream passes to a product recovery section. An alkylated product stream comprising the product aromatic compound is recovered from the product recovery section. A regenerant stream comprising the feed aromatic compound passes to an off-stream selective alkylation reactor containing the solid alkylation catalyst, which is at least partially deactivated. The off-stream selective alkylation reactor operates at regeneration conditions sufficient to at least partially reactivate the solid alkylation catalyst An off-stream reactor effluent stream comprising the feed aromatic compound is recovered from the off-stream selective alkylation reactor. Some of the off-stream reactor effluent stream passes to an off-stream aromatic byproducts removal bed which contains sorbent that contains sorbed aromatic byproducts. At desorption conditions, the aromatic byproducts are at least partially desorbed from the sorbent in the off-stream aromatic byproducts removal bed. An off-stream bed effluent stream comprising the aromatic byproducts and the feed aromatic compound is recovered from the off-stream aromatic byproducts removal bed. Some of the feed aromatic compound in the off-stream bed effluent stream passes to the on-stream selective alkylation reactor. At least intermittently the functions of the on-stream aromatic byproducts removal bed and the off-stream aromatic byproducts removal bed are shifted by operating the off-stream aromatic byproducts removal bed to function as the on-stream aromatic byproducts removal bed and operating the on-stream aromatic byproducts removal bed to function as the off-stream aromatic byproducts removal bed. The functions of the on-stream selective alkylation reactor and the off-stream selective alkylation reactor are also at least intermittently shifted by operating the on-stream selective alkylation reactor to function as the off-stream selective alkylation reactor and operating the off-stream selective alkylation reactor to function as the on-stream selective alkylation reactor.
Other objectives and embodiments of this invention are described in the detailed description.
U.S. Pat. No. 6,069,285 (Fritsch, et al.) describes an alkylation process using two alkylation reactors containing solid catalyst The effluent from the off-stream reactor combines with the effluent from the on-stream reactor, and the combined stream flows to a benzene rectifier.
U.S. Pat. Nos. 5,276,231 (Kocal et al.) and U.S. Pat. No. 5,334,793 (Kocal) describe aromatics removal zones.
U.S. Pat. No. 6,169,219 (Kojima et al.) describes measuring bromine indexes and color in the manufacture of linear alkylbenzenes and linear alkylbenzene sulfonates.